Nervous System Overview

Nervous System

• The nervous system is a complex communication network made of specialized nerve cells called neurons.
• Neurons gather information about the environment, interpret that information, and react to it.
• Neurons are composed of three main regions: dendrites, a cell body, and an axon.
• Dendrites receive impulses from other neurons and send them to the cell body.
• The cell body contains the nucleus and other organelles.
• The axon carries impulses from the cell body to other neurons and muscles.
• There are Three types of neurons: Sensory Neurons, Interneurons, and Motor Neurons.
• Sensory neurons send impulses from receptors in the skin and sense organs to the brain and spinal cord.
• Interneurons relay signals between sensory and motor neurons (found in the spinal cord and brain).
• Motor neurons carry impulses from the brain and spinal cord to glands or muscles, resulting in a response.
• A nerve impulse is also known as an action potential, an electrical charge that travels the length of a neuron.
• The minimum stimulus to cause an action potential is called a threshold.
• When a stimulus reaches the threshold, channels in the plasma membrane open, allowing sodium ions to rapidly move into the cytoplasm.
• The inside of the cell becomes positive, causing other channels to open; potassium ions rapidly leave the cell, restoring a positive charge to the outside of the cell. This reversal moves along the axon like a wave.
• The sodium-potassium pump restores resting potential.
• Many axons have a myelin sheath, an insulating layer that increases the speed of the action potential. The gaps in the myelin sheath are called nodes.
• The speed of an action potential is faster on neurons with a myelin sheath (up to 150 m/s) compared to those without (only 10 m/s).
• Action potentials start when neurotransmitters bind to receptors on the dendrite of a neighboring neuron, which causes channels to open in the neighboring cell, and create a new action potential.
• Neurotransmitters are chemicals that diffuse across a synapse and bind to receptors on the dendrite of a neighboring neuron.
• There are several ways a neurotransmitter is removed from a synapse, including diffusing away from the synaptic cleft, being broken down by enzymes, or being taken back into the neuron by transport proteins.
• Neurons can communicate with many other neurons.

Plant Reproduction

• Reproduction in plants can be sexual or asexual.
• Asexual reproduction, including vegetative reproduction, produces offspring genetically identical to the parent plant.
• Vegetative reproduction uses plant parts to create new plants, such as plantlets growing on plant stems or runners on some plants.
• Examples of vegetative reproduction include gemmae cups found on liverwort tissues, which produce new plants via gemmae.
• Mitosis is a cell division resulting in two identical cells (2n), with the same number of chromosomes.
• Meiosis is a cell division in which four daughter cells with halved (n) chromosomes is produced. The process is involved in plant reproduction.
• The alternation of generations is a life cycle that alternates between a multicellular haploid stage (gametophyte) and a diploid stage (sporophyte)
• In plants, flowers have four main organs–sepals, petals, stamens, and pistils.
• Sepals protect the flower bud, and petals help attract pollinators.
• Stamens are male reproductive organs, composed of filament and anther, and produce pollen grains.
• Pistils are female reproductive organs, containing stigma, style, and ovary that produces ovules.
• Pollinators are animals (e.g., insects, birds, and bats) that transfer pollen from the stamen (male) to the stigma (female).
• Pollination can be self-pollination (within the same plant) or cross-pollination (between different plants).
• Flower adaptations, including color, scent, and nectar production attract pollinators.
• Wind pollination occurs where the flower has lightweight pollen, with stamens below petals and large stigmas.

Flower Adaptations

• Complete flowers have all four organs (sepals, petals, stamens, pistils).
• Incomplete flowers lack one or more essential parts.
• Perfect flowers have both functional stamens and pistils.
• Imperfect flowers have either functional stamens or pistils, but not both.
• The number of flower organs (e.g., sepals, petals, stamens, pistils) distinguishes between monocots (multiple of 3) and dicots (multiple of 4 or 5).

Seed and Fruit Development

• Seeds form following double fertilization when one sperm unites with the egg, and the other combines with two nuclei in the center cell to initiate the development of endosperm, which provides nourishment to the embryo.
• The protective covering around a seed is a seed coat.
• Fruits are primarily formed from the ovary wall and other flower organs.
• Different types of fruit include Simple fleshy fruits (apples, peaches), Aggregate fruits (strawberries, raspberries), Multiple fruits (figs, pineapples), and Dry fruits(pods, nuts, grains).

Seed Dispersal

• Fruits protect and help in seed dispersal and seed dispersal eliminates competition between offspring and their parents for resources.
• Seeds are dispersed by various methods, including wind, water, and animal vectors.